Alerts: Store alert message when raised


The content of each raised alert is stored.

Because the content is stored, the content os no longer recalculated when opening the list of pending alerts.
The original text will always be shown to the user.

The list of pending alerts will include raised alerts where the user has no access to the related item.

In the history of an item, the alert message will contain the title of the item instead of the subject of the alert.